1. Field of the Invention
This invention relates to bearing flushing system for pumps and the like that are exposed to materials that would ruin or degrade the bearings. The bearing flushing system hereof includes a flow restrictor that is designed to permit the passage of flushing water but resist the infusion of contaminants into the bearing surfaces.
2. Description of the Prior Art
Pumps can be designed to handle and move a large quantity of liquids, including those carrying or containing solid materials and liquids that contain corrosives or other materials that would damage the pump if they come in contact with the bearing surfaces between the housing and the shaft or impeller. For example, pumps have been developed which move municipal sludge or other sediment-containing slurries having a large quantity of suspended solids such as twigs, rags, glass, grit, or sand. In many industrial applications, pumps must handle highly corrosive acids.
A pump useful in such environments is shown in U.S. Pat. No. 4,063,849 entitled Non-Clogging, Centrifugal, Coaxial Discharge Pump. The pump disclosed therein is designed to be at least partially submerged in fluid containing sediment or sludge. It includes a centrally located, normally vertically oriented shaft for driving the impeller, at least one of the bearing surfaces for the shaft being located below the water level of the fluid to be pumped.
In order to isolate the bearing surfaces from such contaminants, and to lubricate and cool the bearing surfaces, water has been employed as a medium to flush the bearing surfaces. Water is injected into the bearing surfaces at a pressure higher than the internal pressure of the pump. This is designed to ensure a positive flow of cleansing and lubricating fluid to the bearing surfaces. The bearings are designed with a lubricating groove or grooves that pass through the entire length of the bearing surfaces. The water thus is permitted to flow through the bearing and to pass through the other components of the system.
U.S. Pat. No. 4,462,751 entitled Centrifugal Pump Improvement discloses a pump for moving liquids but does not specifically recite any bearing flushing system. U.S. Pat. No. 4,877,371 entitled Pump, discloses a pump for moving dirty, viscous, hazardous or corrosive liquids but positions one of the pump bearings away from the liquid and does not provide for flushing lower bearings which may be submerged in the liquid.
However, when the pump is at least partially submerged such that one or more of the bearings is below the surface level of the pumped medium, there is a substantial risk that backflow of the pumped medium may contaminate the bearing surface with grit, sand, acid or the like. Maintaining the water flow to flush the bearings when the pump is not operating may be expensive both in terms of the expense of the water and the labor necessary to monitor the flushing operation. If the water supply to flush the bearing is stopped or interrupted, the backflow of contaminants may enter the bearing, leaving grit or the like which is extremely difficult to remove without disassembling the pump and removing the bearing. Given that such pumps often move sewage or sludge and may be extremely large, this is a situation to be avoided if at all possible.
Accordingly, there has developed a real need for a backflow restrictor which can be used in connection with a flushing system for pumps. Such a flow restrictor must allow clean flushing water to flow into the bearing and through the seal, but resist the entry of the pumped medium, and especially suspended particulates, into the bearing surfaces. Yet further, there has developed a need for a bearing flushing system that will reduce the amount of flushing water required and, when the flow of flushing water is discontinued, resist the entry into the bearing surfaces not only of small solids carried by the liquid but of contaminating liquids such as acids or other corrosives as well. Such a seal must nonetheless be compatible with existing pump systems so that radical modifications are not necessary to accommodate such a system. In particular, a bearing flushing system must be able to withstand exposure to and resist entry of contaminant liquids when some of the components of the flushing system are in direct contact with the contaminant liquid and submerged therein, but nonetheless admit the passage of flushing liquid therethrough.